1. Field of the Invention
The present invention relates to an irradiation display apparatus which displays an image by radiating beam light two-dimensionally and a technology of detecting an inclination and a surface shape of an irradiated surface and correcting an image distortion.
2. Background Art
In recent years, light emitting diodes such as LEDs and laser light sources have been used as light sources of three primary colors of RGB (Red, Green and Blue), and projection type image display apparatuses (hereinafter, referred to as “projector”) which form an image by raster-scanning the light emitted from the light sources have attracted attention.
For example, the projector includes three laser light sources of three primary colors of RGB, a collimator lens which approximately collimates a light emitted from each laser light source, a synthesizing prism which synthesizes the approximately collimated laser light of each color, and a reflection angle variable mirror such as an MEMS mirror which two-dimensionally scans the synthesized laser light. The laser light source of each color is modulated and driven in synchronism with an inclination angle of the reflection angle variable mirror depending on an image to be formed, and the modulated laser light is reflected by the reflection angle variable mirror and an irradiation screen is scanned by the modulated laser light so as to perform an image display. Since the laser light is approximately collimated, even if a distance to a projected surface changes, it is possible to display an image of a good quality rarely being out-of-focus.
However, since there is a beam waist in laser light in practice and an angular speed of the reflection angle variable mirror is constant, in a case of displaying an image at a distance different from a predetermined irradiation distance, the size of a beam spot of the laser light is not coincident with the pixel pitch of an image and thus an image of a good quality is not obtained. Particularly, in a case where laser light is radiated obliquely onto an irradiation screen, an image distortion such as a trapezoidal distortion occurs.
Therefore, it is necessary to measure an irradiation distance to the irradiation screen and to perform a correction depending on the distance in order to display an image of a good quality. JP-A-2008-268645 discloses a configuration in which a two-dimensional position sensitive light detector (PSD) which detects a light amount centroid of a light spot is provided, the sensor receives the light which is reflected and scattered on a projected surface of laser light scanned by the reflection angle variable mirror, a distance between a main body of an image projection apparatus and a projected object is calculated from obtained position information, and the position of a beam waist in divergent angle changing means is optimized based on the calculation result, and this configuration enables an image projection of a good quality.